Taxonomy & naming
Steindachnerina amazonica was described by the Austrian ichthyologist Franz Steindachner in 1911. It belongs to the genus Steindachnerina within the family Curimatidae — the toothless characins, a large Neotropical group placed in the order Characiformes alongside the piranhas, pacus and silver dollars of Serrasalmidae, though curimatids are unrelated to that predatory and plant-eating lineage in diet or dentition. The genus itself was later named in honour of Steindachner by subsequent workers, so the species carries his name twice over, once as author and once embedded in the genus.
Curatorial work on Steindachnerina has continued well past the original description; a Rio Tocantins study formally documenting new species in the genus confirms the Tocantins drainage as part of the known range for material referred to S. amazonica, and underscores that curimatid taxonomy in this genus remains an active area of description and revision. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the authority for the currently valid combination, and this account follows that placement without alteration.
Morphology
Steindachnerina amazonica is a small, laterally compressed characin with the streamlined, silvery build typical of Curimatidae — a fusiform body, a small subterminal or ventrally positioned mouth adapted for grazing rather than biting, and no functional jaw teeth, a defining feature of the family that separates it sharply from the toothed, blade-jawed piranhas sharing its order. FishBase records a maximum published length of 4 in standard length for the species, making it one of the smaller curimatids and a genuinely compact fish by any characin standard.
Colouration is unremarkable but functional: a silvery body with a faint dark lateral stripe or series of scale markings typical of small shoaling curimatids, countershaded to blend into open, sediment-laden water. There is no striking pattern or fin extension to speak of — this is a fish built for moving in tight groups over the bottom, not for display.
Habitat
The species is recorded from the Tocantins River basin in Brazil, a major Amazonian tributary system, where it occupies tropical freshwater habitat and is described as benthopelagic — spending its time near the bottom and just above it, consistent with its detritus-and-biofilm feeding habit. As with many curimatids, it is likely associated with slower-flowing river margins, floodplain channels and sediment-rich stretches where fine organic material accumulates, though the cache does not provide detailed microhabitat data beyond the basin-level record.
Specific pH, hardness and temperature figures for wild populations are not available in the sources reviewed for this account; broadly, Tocantins basin waters are warm, tropical lowland river conditions typical of the wider Amazon system, and this account does not extrapolate beyond what FishBase and the supporting literature confirm.
Feeding
Steindachnerina, like the rest of Curimatidae, is a detritivore rather than a predator or plant-shredder. A detritivory study covering the genus confirms that Steindachnerina species feed on slime films — the mixed diatom, algae, zooplankton and detrital layer that coats submerged surfaces and sediment — and documents a notably high intestinal quotient (around 9.46) in the genus, reflecting a gut specialised for processing large volumes of difficult-to-digest detrital matter rather than protein-dense prey. The same research frames this feeding strategy as one of several ways curimatids partition food resources within the Amazon basin, alongside algae-grazing and zooplankton-focused relatives.
In practical terms this makes S. amazonica an ecological equivalent to a small aquatic vacuum cleaner, continuously processing fine organic material rather than hunting, browsing live plants or taking large prey items — a sharp contrast to the predatory Brycon or the plant-destructive silver dollars found elsewhere in this same order.
Mating
No courtship or pairing behaviour specific to Steindachnerina amazonica is documented in the sources reviewed for this account. General characin husbandry guidance notes that egg-scattering species typically spawn in response to a rise in temperature and softer, more acidic water conditions that mimic seasonal flooding, with no pair bond beyond the act of spawning itself, but this is a family-level generalisation rather than a confirmed observation for this species, and no external sexual dimorphism is documented for it.
Breeding
Curimatidae, including Steindachnerina, are characins, and general characin breeding accounts describe the group as external-fertilising egg-scatterers: eggs are released into open water or over fine-leaved vegetation with no parental care, in contrast to the substrate-guarding piranhas or the foam-nest-building Hepsetus found elsewhere in this order. Hobby breeding guidance for egg-scattering characins notes that soft, peat-filtered acidic water can help induce spawning, with eggs hatching in roughly 24–30 hours and fry taking micro-foods before graduating to brine shrimp nauplii.
However, no source reviewed here documents an actual observed or aquarium spawning of Steindachnerina amazonica specifically, and this species is not established as a regularly bred aquarium fish. This account presents the egg-scattering mode as the best-supported characin-family expectation rather than a confirmed record for the species, and treats its breeding biology in captivity as effectively undocumented.
In the aquarium
Steindachnerina amazonica is rarely, if ever, seen in the aquarium trade, and no dedicated hobby care literature for the species was found in the sources reviewed. What can be said with confidence follows from its biology: at under 4 in and shoaling by nature, it would need to be kept in a group rather than singly, in a tank offering open swimming space over a soft substrate where it could forage, with tankmates too large to see it as prey and none large enough to prey on it in turn. Its detritivorous diet suggests it would do well in a mature, established aquarium with some accumulated biofilm and organic matter to graze, supplemented with sinking foods, algae wafers or similar prepared diets rather than a purely predatory or plant-based menu.
Because it is not established in the hobby, prospective keepers should treat any specimen offered for sale with caution regarding correct identification — curimatids are frequently confused with one another and with unrelated small silver characins — and should not expect readily available husbandry data beyond the general characin baseline described above.
Conservation
The IUCN Red List assesses Steindachnerina amazonica as Least Concern, per FishBase's summary of that assessment (dated 2018), reflecting a lack of documented major threats to the species within its known Tocantins basin range. As with many small, non-commercial Amazonian characins, the primary long-term watch items are basin-scale pressures common to the wider region — damming, deforestation-linked sedimentation and water-quality change in the Tocantins system — rather than any species-specific exploitation, since S. amazonica is not a significant target of fisheries or the aquarium trade.